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arXiv · 2505.01127

Towards a critical endpoint in the valence fluctuating Eu(Rh$_{1-x}$Co$_{x}$)$_2$Si$_2$ system

Franziska Walther·Michelle Ocker·Alexej Kraiker·Nubia Caroca-Canales·Silvia Seiro·Kristin Kliemt·Cornelius Krellner
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Abstract

We report on the successful single crystal growth of pure EuRh${_2}$Si${_2}$ and of Eu(Rh$_{1-x}$Co$_{x}$)$_2$Si$_2$ with $x\leq0.23$ by the flux method. Through Co substitution, EuRh$_2$Si$_2$ can be tuned from stable antiferromagnetism via a valence-transition state towards the valence-crossover regime. From magnetization measurements, we constructed a $B - T$ phase diagram for EuRh${_2}$Si${_2}$ comprising multiple magnetic phases and showing a sizable magnetic anisotropy within the basal plane of the tetragonal unit cell. This indicates a complex antiferromagnetic ground state for $x=0$. By applying positive chemical pressure through the substitution series Eu(Rh$_{1-x}$Co$_{x}$)$_2$Si$_2$, a sharp temperature-induced first-order phase transition is observed in magnetization, resistivity and heat capacity for 0.081 $\leq$ $x$ $\leq$ 0.119. The critical end point of this valence transition is located in the phase diagram in the vicinity of 0.119 $<x_{\rm EDX}<$ 0.166. At higher substitution level, the system reaches a valence-crossover regime. The obtained results are presented in a temperature-substitition phase diagram.

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Franziska Walther, Michelle Ocker, Alexej Kraiker, Nubia Caroca-Canales, Silvia Seiro, Kristin Kliemt, Cornelius Krellner. 2025-05-02. Towards a critical endpoint in the valence fluctuating Eu(Rh$_{1-x}$Co$_{x}$)$_2$Si$_2$ system. https://arxiv.org/abs/2505.01127

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